K. Ching Man

Preoperative Amiodarone as Prophylaxis against Atrial Fibrillation after Heart Surgery

Background Atrial fibrillation occurs commonly after open-heart surgery and may delay hospital discharge. The purpose of this study was to assess the use of preoperative amiodarone as prophylaxis against atrial fibrillation after cardiac surgery. Methods In this double-blind, randomized study, 124 patients were given either oral amiodarone (64 patients) or placebo (60 patients) for a minimum of seven days before elective cardiac surgery. Therapy consisted of 600 mg of amiodarone per day for seven days, then 200 mg per day until the day of discharge from the hospital. The mean (±SD) preoperative total dose of amiodarone was 4.8±0.96 g over a period of 13 ± 7 days. Results Postoperative atrial fibrillation occurred in 16 of the 64 patients in the amiodarone group (25 percent) and 32 of the 60 patients in the placebo group (53 percent) (P = 0.003). Patients in the amiodarone group were hospitalized for significantly fewer days than were patients in the placebo group (6.5 ± 2.6 vs. 7.9 ± 4.3 days, P = 0.04). ...

Effect of Atrial Fibrillation on Atrial Refractoriness in Humans

BACKGROUND The acute effect of atrial fibrillation (AF) on the atrial effective refractory period (ERP) in humans is unknown. METHODS AND RESULTS In 20 patients without structural heart disease, the atrial ERP was measured before and after pacing-induced AF at drive cycle lengths of 350 and 500 ms. Immediately after spontaneous AF conversion, the post-AF ERP was measured. The pre-AF ERPs at 350 and 500 ms were 206 +/- 23 and 216 +/- 17 ms, respectively. The time to spontaneous conversion of AF was 7.3 +/- 1.9 minutes. The first post-AF ERPs at drive cycle lengths of 350 and 500 ms were 175 +/- 30 ms (P < .0001 versus pre-AF) and 191 +/- 30 ms (P < .0001 versus pre-AF), respectively. The post-AF ERP returned to the pre-AF ERP value after a mean of 8.4 +/- 0.3 minutes. In 15 patients, during the determination of the post-AF ERP, secondary episodes of AF lasting 1 +/- 1.5 minutes were reinduced 6 +/- 3 times per patient. There was a significant inverse logarithmic relationship between the time to reinduction of AF and the duration of secondary episodes of AF (P < .0001, r = 5). CONCLUSIONS In humans, several minutes of induced AF is sufficient to shorten the ERP for up to approximately 8 minutes. The temporal recovery of the ERP is reflected in progressively shorter episodes of reinduced AF. These data imply that AF transiently shortens the atrial wavelength and suggest a mechanism by which AF may perpetuate itself.

Effect of an irregular ventricular rhythm on cardiac output

Impairment of cardiac function in atrial fibrillation has been attributed to loss of atrial contraction and to a rapid ventricular rate. The results of this study suggest that irregularity of the ventricular rhythm, independent of the ventricular rate, may also contribute to impairment of cardiac function during atrial fibrillation.

Radiofrequency Catheter Modification of Atrioventricular Conduction to Control the Ventricular Rate during Atrial Fibrillation

BACKGROUND In some patients with atrial fibrillation, the ventricular rate may be difficult to control with medications. We evaluated a radiofrequency catheter technique to modify atrioventricular conduction in atrial fibrillation in order to control the ventricular rate without creating pathologic atrioventricular block. METHODS We studied 19 consecutive patients with atrial fibrillation and uncontrolled ventricular rates refractory to drug therapy. They had had atrial fibrillation for a mean (+/- SD) of 5.5 +/- 4.9 years, had had 4.9 +/- 0.9 unsuccessful drug trials, and were 62 +/- 15 years old. Before the procedure, the maximal ventricular rate during exercise was 180 +/- 39 beats per minute. A total of 11 +/- 5 radiofrequency-energy applications were delivered to the posterior septal or midseptal right atrium, near the ostium of the coronary sinus. RESULTS Successful control of the ventricular rate without pathologic atrioventricular block was achieved in 14 of the 19 patients (74 percent). Persistent third-degree atrioventricular block requiring a permanent pacemaker occurred inadvertently in four patients (21 percent). Atrioventricular conduction was intentionally ablated in one patient. The 14 patients who had successful modification of conduction had persistent reductions in maximal ventricular rate during exercise (rate at three months, 126 +/- 24 beats per minute; P < 0.01). These patients had resolution of symptoms related to rapid rates during 8 +/- 2 months of follow-up. One patient had a recurrence of a rapid ventricular rate but was again asymptomatic after a second modification procedure. One patient with dilated cardiomyopathy died suddenly, five months after a successful procedure. CONCLUSIONS A catheter technique to modify atrioventricular conduction without creating pathologic atrioventricular block is feasible in the majority of patients with symptomatic atrial fibrillation and a rapid ventricular rate refractory to drug therapy.

Effect of Verapamil and Procainamide on Atrial Fibrillation–Induced Electrical Remodeling in Humans

BACKGROUND Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The purpose of this study was to determine the effect of verapamil and procainamide on these manifestations of AF-induced electrical remodeling. METHODS AND RESULTS In adult patients without structural heart disease, the atrial ERP was measured before and after AF after pharmacological autonomic blockade and administration of verapamil (17 patients), procainamide (10 patients), or saline (20 patients). AF was then induced by rapid pacing. Immediately on AF conversion, the post-AF ERP was measured at alternating drive cycle lengths of 350 and 500 ms. In the saline group, the pre-AF and first post-AF ERPs at the 350-ms drive cycle length were 206+/-19 and 179+/-27 ms (P<.0001), respectively, and at the 500-ms drive cycle length, the values were 217+/-16 and 183+/-23 ms, respectively (P<.0001). There was a similar significant shortening of the first post-AF ERP in the procainamide group. In the verapamil group, however, there was no difference between the pre-AF and the first post-AF ERP at the 350-ms (226+/-15 versus 227+/-22 ms, P=.8) or 500-ms (230+/-17 versus 232+/-20 ms, P=.6) drive cycle length. During determinations of the post-AF ERP, 105 secondary episodes of AF were unintentionally induced in 12% of verapamil patients compared with 90% and 80% of saline and procainamide patients (P<.01 versus verapamil). CONCLUSIONS Pretreatment with the calcium channel antagonist verapamil, but not the sodium channel antagonist procainamide, markedly attenuates acute, AF-induced changes in atrial electrophysiological properties. These data suggest that calcium loading during AF may be at least partially responsible for AF-induced electrical remodeling.

A Prospective Evaluation of Catheter Ablation of Ventricular Tachycardia as Adjuvant Therapy in Patients With Coronary Artery Disease and an Implantable Cardioverter-Defibrillator

BACKGROUND Implantable cardioverter-defibrillator (ICD) therapy is integral to current therapy for ventricular tachycardia. Patients with an ICD frequently require concomitant antiarrhythmic drug therapy. Despite this, some patients still receive frequent ICD therapies for ventricular tachycardia. Therefore, the purpose of this prospective study was to determine the utility of ablation of ventricular tachycardia in patients with an ICD who experience frequent ICD therapies. METHODS AND RESULTS Twenty-one consecutive patients with frequent ICD therapies despite antiarrhythmic drug therapy were the subjects of this study. The mean age was 69+/-6 years, and 17 were men. The mean ejection fraction was 0.22+/-0.08, and all patients had coronary artery disease. During the 36+/-51 days (range, 4 days to 7 months) preceding the ablation procedures, the patients received 34+/-55 ICD therapies for the clinical ventricular tachycardia, or a mean of 25+/-88 ICD therapies per month. The patients underwent radiofrequency ablation of the presumed clinical ventricular tachycardia by inducing the tachycardia and mapping according to endocardial activation, continuous electrical activity, pace mapping, concealed entrainment, or mid-diastolic potentials. Ablation of the clinical arrhythmia was successful in 76% of patients during 1.4+/-0.6 (range, 1 to 3) ablation procedures and required 12.5+/-9.2 applications of energy. During 11.8+/-10.0 months of follow-up, the frequency of ICD therapies per month decreased from 60+/-80 before successful ablation to 0.1+/-0.3 ICD therapies per month after ablation (P=.01). A quality-of-life assessment demonstrated a significant improvement after successful (P=.02) but not unsuccessful ablation (P=.9). CONCLUSIONS Radiofrequency ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an ICD has a reasonable success rate, significantly reduces ICD therapies, and appears to be associated with an improved quality of life.

Effect of Ventricular Shock Strength on Cardiac Hemodynamics

Ventricular Defibrillation and Cardiac Function. Introduction: The effect of implantable defibrillator shocks on cardiac hemodynamics is poorly understood. The purpose of this study was to test the hypothesis that ventricular defibrillator shocks adversely effect cardiac hemodynamics.

Long-term follow-up after radiofrequency modification of the atrioventricular node in patients with atrial fibrillation.

OBJECTIVES The purpose of this study was to describe the long-term follow-up results in 62 patients with atrial fibrillation and an uncontrolled ventricular rate, who underwent radiofrequency modification of the atrioventricular (AV) node. BACKGROUND Previous studies in small numbers of patients have suggested that radiofrequency modification may be effective in controlling the ventricular rate in patients with atrial fibrillation, but long-term follow-up data have been lacking. METHODS The subjects of this study were 62 consecutive patients (mean age +/- SD 65 +/- 14 years; 43 with structural heart disease) who underwent an attempt at radiofrequency modification of the AV node because of symptomatic, drug-refractory atrial fibrillation with an uncontrolled ventricular rate. The atrial fibrillation was chronic in 46 patients and paroxysmal in 16. Radiofrequency energy was applied to the posteroseptal or mid-septal right atrium to lower the ventricular rate in atrial fibrillation to 120 to 130 beats/min during an infusion of 4 micrograms/min of isoproterenol. RESULTS Short-term control of the ventricular rate was successfully achieved without the induction of pathologic AV block in 50 (81%) of 62 patients. Inadvertent high degree AV block occurred in 10 (16%) of 62 patients, with the AV block occurring at the time of the procedure in 6 patients and 36 to 72 h after the procedure in 4. During 19 +/- 8 months of follow-up (range 4 to 33), 5 (10%) of 50 patients had a symptomatic recurrence of an uncontrolled rate during atrial fibrillation. Overall, adequate rate control at rest and during exertion, without pathologic AV block, was achieved long term in 45 (73%) of 62 patients. Among 37 patients with a successful outcome, left ventricular ejection fraction increased from (mean +/- SD) 0.44 +/- 0.14 to 0.51 +/- 0.10 one year later (p < 0.001). Complications other than AV block included polymorphic ventricular tachycardia 10 to 24 h after the procedure in two patients who had a predisposing factor for ventricular tachycardia and sudden death 1 to 5 months after the procedure in two patients with idiopathic dilated cardiomyopathy, one of whom had a pacemaker for AV block. CONCLUSIONS In approximately 70% of properly selected patients with atrial fibrillation and an uncontrolled ventricular rate, radiofrequency modification of the AV node results in excellent long-term control of the ventricular rate at rest and during exertion.

Short-Term Effect of Atrial Fibrillation on Atrial Contractile Function in Humans

BACKGROUND Conversion of chronic atrial fibrillation (AF) is associated with atrial stunning, but the short-term effect of a brief episode of AF on left atrial appendage (LAA) emptying velocity is unknown. The purpose of this study was to determine whether a short episode of AF affects left atrial function and whether verapamil modifies this effect. METHODS AND RESULTS The subjects of this study were 19 patients without structural heart disease undergoing an electrophysiology procedure. In 13 patients, LAA emptying velocity was measured by transesophageal echocardiography in the setting of pharmacological autonomic blockade before, during, and after a short episode of AF. During sinus rhythm, the baseline LAA emptying velocity was measured 5 times and averaged. AF was then induced by rapid right atrial pacing. After either spontaneous or electrical conversion, LAA emptying velocity was measured immediately on resumption of sinus rhythm and every minute thereafter. The mean duration of AF was 15.3+/-3.8 minutes. The mean baseline emptying velocity was 70+/-20 cm/s. The first post-AF emptying velocity was 63+/-20 cm/s (P=0.02 versus baseline emptying velocity). The post-AF emptying velocity returned to the baseline emptying velocity value after 3.0 minutes. The mean percent reduction in post-AF emptying velocity was 9.7+/-21% (range, 15% increase to 56% decrease). A second group of 6 patients were pretreated with verapamil (0.1-mg/kg IV bolus followed by an infusion of 0.005 mg. kg-1. min-1). In these patients, the first post-AF emptying velocity, 58+/-14 cm/s, was not significantly different from the pre-AF emptying velocity, 60+/-13 cm/s (P=0.08). CONCLUSIONS In humans, several minutes of AF may be sufficient to induce atrial contractile dysfunction after cardioversion. When atrial contractile dysfunction occurs, there is recovery of AF within several minutes. AF-induced contractile dysfunction is attenuated by verapamil and may be at least partially mediated by cellular calcium overload.

Radiofrequency catheter ablation of inappropriate sinus tachycardia guided by activation mapping.

OBJECTIVE The purpose of this study was to evaluate the value of activation mapping for radiofrequency modification of the sinus node and the long-term success rate of the procedure in a series of patients with inappropriate sinus tachycardia. BACKGROUND The results of radiofrequency ablation of inappropriate sinus tachycardia have been reported in only a small number of patients. METHODS The subjects of this study were 29 consecutive drug-refractory patients who underwent catheter ablation of inappropriate sinus tachycardia. Target sites were selected by activation mapping during sinus tachycardia. RESULTS The ablation procedure was successful acutely in reducing the baseline sinus rate to <90/min and the sinus rate during isoproterenol infusion by >20% in 22 of 29 patients (76%). In 13 of 22 patients (59%) with a successful acute outcome, successive applications of radiofrequency energy at the site of earliest endocardial activation resulted in a cranial-caudal migration of earliest endocardial activation from the high lateral right atrium, along with a step-wise reduction in heart rate. In the other nine patients (41%) with a successful acute outcome, the reduction in sinus rate occurred abruptly, unaccompanied by migration of the site of earliest activation. Symptoms due to inappropriate sinus tachycardia recurred at a mean of 4.4+/-; 3 months after the ablation procedure in 6 of 22 patients (27%). After additional procedures in three patients, symptoms of inappropriate sinus tachycardia ultimately were successfully eliminated over the long-term in 19 of 29 patients (66%). CONCLUSIONS In conclusion, radiofrequency ablation is at best only modestly effective for managing patients with inappropriate sinus tachycardia. The two different responses of heart rate to radiofrequency ablation may reflect differences in the number and/or multicentricity of subsidiary sites of impulse generation within the sinus node and/or atrium in patients with inappropriate sinus tachycardia.